Arc plasma generators

ABSTRACT

A plasma generator comprises a torch in which a spacer made of a refractory material and having a central opening in which the cathode is fitted and a concentric ring of peripheral openings which serve to feed the plasma gas into the arc chamber of the torch in uniformly distributed fashion is provided in the interior of the anode unit. Suitably the spacer is of disc-shape with a concentric ring of equally spaced openings extending axially through it.

121-l+-71 XR 356289079 72] Inventors David John Miller Dobbs; [50] Field 0! Search 219/74, 75, Derek Linder; Leslie John Giles; Joseph 12] R, 121 P; 313/231 Kenneth Hill, all of London, England [21] Appl. No. 8,249 [56] References Cited [22] Filed Feb. 3, 1970 UNITED STATES PATENTS [451 Famed Dec-14,1971 2,858,412 l0/l958 Kane et al 219/75 [731 8 British Railways B08"! 3,238,349 3/1966 Anderson et al 219/75 London, England [32] Priority Feb. 20, 1969 Pnmary Examiner-Raymond F. Hossfeld 3 Great Britain Attorney-Sommers & Young 1 9359/69 ABSTRACT: A plasma generator comprises a torch in which a l 54] ARC PLASMA GENERATORS spacer made of a refractory material and having a central 3 Claims 2 Drawing Figs opening in which the cathode is fitted and a concentric ring of peripheral openings which serve to feed the plasma gas into [52] 1.8- CI .1 313/231, the arc chamber of the rch in uniformly distributed fashion 219/75, 219/121 P is provided in the interior of the anode unit. Suitably the [51] Int. "I s acer is of disc shape with a concentric ring of equally spaced openings extending axially through it.

ARC PLASMA GENERATORS This invention concerns improvements relating to are plasma generators, especially such used for improving wheelrail adhesion of railway vehicles by cleaning the rails or rails and wheels.

The characteristics of a DC are plasma generator or torch in which a cathode is mounted coaxially in a cylindrical anode unit are very sensitive to the accuracy of coaxial alignment of the two electrodes.

Even when the cathode has been accurately centered in the anode, the severe vibration and shock to which a plasma torch is subjected when mounted on a locomotive or other vehicle for rail-cleaning purposes can cause displacements which adversely affect torch operation and ultimately torch life. As an illustration of the effect of such displacement, reference may be made to the following example: If, with a conventional torch operating with a current of 250 amperes and a flow of 50 liters per minute of gas comprising 90 percent argon and l percent hydrogen, the nominal working voltage is 45 volts, a displacement of the cathode, say due to shock, from the central position by as little as one-hundredth of an inch may cause the voltage to fall to a value of the order of 15 volts.

Cathode vibration and displacement can be minimized by rigid construction and/or the insertion of insulating spacers to hold the cathode. Such measures do not however overcome the need for accurate positioning of the cathode with respect to the anode, conventionally by a micrometer-screw adjustment. The present invention seeks to obviate the difficulties and to simplify the manufacture and assembly of plasma torches.

According to the invention, plasma generator comprises a torch wherein a spacer made'of a refractory material and having a central opening in which the cathode is fitted and a concentric ring of peripheral openings which serve to feed the plasma gas into the arc chamber of the torch in uniformly distributed fashion is provided in the interior of the anode unit.

An embodiment of the invention by way of example will now be more fully described with reference to the accompanying drawing, in which:

FIG. 1 is a diagrammatic axial section through the cathodeanode assembly of a plasma-arc torch, and

FIG. 2 a cross section on the line 11-" in F IG. 1.

In the drawing, the cathode of the torch is indicated at 1 and part of the anode unit at 2. Between them there is a discshaped spacer 3 made of a refractory material, for example of an asbestos or ceramic material, and having a flange 4 by which it rests on an annular shoulder 5 in the anode unit 2. A hublike part 6 of the spacer fits into an upper portion of the arc chamber 7 below the said shoulder. The whole spacer is penetrated by a concentric ring of axially extending round holes 8 and by an axial round hole 9 for the cathode 1, whose free end is located just above the nozzle 10 of the torch. The ring of holes 8 is located at about the midwidth of the annular space between the cathode l and the wall of the chamber 7 in the anode unit.

The hole 9, in which the cathode l is a tight fit, need ensure only that the position of the cathode satisfies minimum requirements as to mechanical alignment. The number, size and exact disposition of the peripheral holes 8 can be varied to suit the particular requirements. Typically and as shown, eight holes equally spaced around the hole 9 can be used. The size of the holes 8 is important. Too small or too large a hole may produce a loss in the stabilizing properties, as a gas distributor, of the spacer.

By way of illustration, with a cathode 1 having a diameter of one-fourth inch and an arc chamber 7 having a diameter of five-eighth inch, a suitable provision of holes 8 would be a ring of eight holes each of one-sixteenth inch diameter spaced equally around a circle of seven-sixteenths inch diameter.

Without such a spacer 3 and its ring of gas-distributing holes 8, the only impedance presented to the gas flow would be offered by the annulus between the cathode l and anode 2. This would only produce uniform gas distribution and stable arc characteristics if the cathode were accurately coaxial. With the spacer 3, however, each hole 8 presents a constant impedance to the gas flow irrespective of any minor departure of the cathode from coaxiality with the anode. Thus, a uniform gas feed is presented to the arc with resultant uniformity and stability of characteristics. By simple means, the need for accurate electrode disposition in the torch is eliminated and the torch is rendered largely immune to vibration and shock. Thus, for instance, if a torch such as has been described is operated under the same electrical and flow conditions as are set out in the illustration previously given for a conventional torch, a working voltage of 45 volts 5 volts can be obtained without the necessity for precision setting of the cathode or accurate symmetry of its tip, the perfonnance being also substantially unaffected by displacements due to mechanical shock. Finally by preventing the torch from operating in undesirable manner due to electrode shift, the life of the torch may be lengthened.

We claim:

1. A plasma generator comprising a torch including a cathode and an anode with an arc chamber, wherein a spacer made of a refractory material and having a central opening in which the cathode is fitted and a concentric ring of equally spaced substantially axially extending openings spaced from the said cathode and anode which serve to feed the plasma gas into the arc chamber in uniformly distributed fashion is provided in the interior of the anode and extends into the arc chamber.

2. A generator according to claim 1, wherein the spacer has a flange by which it rests on an annular shoulder in the anode and a hublike part by which it fits into the arc chamber.

3. A generator according to claim 1, wherein the ring of openings in the spacer is located substantially at the midwidth of the annular space between the cathode and the wall of the arc chamber. 

1. A plasma generator comprising a torch including a cathode and an anode with an arc chamber, wherein a spacer made of a refractory material and having a central opening in which the cathode is fitted and a concentric ring of equally spaced substantially axially extending openings spaced from the said cathode and anode which serve to feed the plasma gas into the arc chamber in uniformly distributed fashion is provided in the interior of the anode and extends into the arc chamber.
 2. A generator according to claim 1, wherein the spacer has a flange by which it rests on an annular shoulder in the anode and a hublike part by which it fits into the arc chamber.
 3. A generator according to claim 1, wherein the ring of openings in the spacer is located substantially at the midwidth of the annular space between the cathode and the wall of the arc chamber. 